Since I said “Yes” from the request of the student who was suffering from choosing her major and asked me whether I could write for advising some students how to choose his/her major, it is my pleasure to share my experience to choose my major when I was young. Some part of this article was also taken from my statement of purpose that I wrote to apply for Stanford.In high school, studying the unimaginably small world of atoms and molecules appealed to me in such a great manner that I chose to study chemistry in depth in college. My goal was to be able to control the atoms and molecules. My priority was to get in to the Department of Chemistry at POSTECH, which has the strongest academic credential and has been developed into one of the most successful universities in Asia despite its short history (I know you know). I tried my best to get into POSTECH, and my hard work paid off when I received a high score on the Korean SAT and was accepted by the Department of Chemistry at POSTECH. During my early undergraduate years (1st and 2nd years), I rather focused on extracurricular activities than studying my major chemistry. However, it was so lucky that I could join the chemistry undergraduate research programs because I found what appealed to me. I found myself being very interested in X-ray crystallography, which enables to visualize the true structures of small molecules. Thus, Inorganic Chemistry came to me. Moreover, I was so fascinated by the beauty of the single crystals and so excited to anticipate its structure through X-ray crystallography when my crystal grew. I continued my master’s degree in the same laboratory. Again, it was fortunate for me to be able to find areas where I love through POSTECH's unique undergraduate research program. As you may know, in POSTECH, there are so many undergraduate research programs that you can join. I hope that these programs may help you to find what you like.After obtaining my master's degree, I decided to study organometallic chemistry for my PhD at Stanford. Since fluorine atom has been used in the medicinal chemistry due to its intrinsic property associated with the radioactive isotope 18F, I studied to make carbon-fluorine bonds. After my PhD study, I indeed worked on radiochemistry dealing with 18F at Harvard. Finally, some delicious outcomes from the study gave me an opportunity that I returned to my school as an assistant professor, which was an honorable moment to me. In fact, the process of making carbon-fluorine bonds during my Ph.D. study was so difficult and very frustrating, but I have overcome such a difficult situation with a strong belief that there is no impossible, a positive thinking that I can do it. Thus, my hard work was finally paid off from great results during my post-doctoral career and I realized again that doing one’s best will always be paid off at the end.The most important job at POSTECH is to deliver what I have been learning for past 15 years to POSTECH students. Of course, that is a role of any professor, but above all, I am a senior of these undergraduates who loves POSTECH. Thus, I have been enjoying chatting with many undergraduate students for the past five years. In my research lab, of course, my priority is to investigate new field with graduate students. Therefore, I also like to discuss any research with them very informally so that they can build up the potential to create new field eventually. I really wish all the students in POSTECH have a successful career during their study. Unlike myself who have already chosen the department when I joined POSTECH, I believe that many of the current freshmen at POSTECH are going to worry about which department they should choose. Therefore, it is going to be one of good ways to participate actively in the programs introduced by the departments at POSTECH and to consult with the professors and seniors in the department that you may be interested since all the departments are creating programs for helping the students who worry about selecting the department. However, above all, I suggest the freshman participate the undergraduate research programs in the first year. It would be the most important for a freshman to find a department where he or she is really interested in from the true experience that the freshman has through the undergraduate research programs that all departments have from the first grade, you will find what you really like.Therefore, although I have written many stories here, the most important thing for you is finding an area where you can really enjoy it. Sometimes I find that some undergraduate students worry about their careers after graduation, but I have never seen anyone who cannot get a job after graduation. I have hardly seen any Postechian who suffers from studying the field that he or she is having a fun. Choosing a major will not be so difficult if you remember the most enjoyable and memorable moments when you know the field where you have an experience from various classes or various research/experimental labs.